Facsimile transmission of information is becoming an essential form of communication in business and government because of its time saving advantages.
A facsimile communication system operates in the following manner. After the transmitter and receiver connection has been initialized, a facsimile machine scans a page, scanning about 200 line pixels/inch, thus converting pixels to a series of ones and zeros. After a page is scanned, the pixel information is transmitted through telephone lines to a remote receiving facsimile machine. After a page of pixel information is received at the remote facsimile machine, several seconds are spent as the receiving machine sends to the transmitting machine a positive confirmation that the transmission has been received. If something happens in the middle of a page transmission, the transmitting facsimile machine will not be able to detect that there is a problem until after the entire page is transmitted. Furthermore, if the transmitting machine does not receive the positive confirmation, then the transmitting machine disconnects itself from the telephone line, and thus ends the transmission of the information. To effect transmission, a user must then resend the transmission, thus re-initializing the transmitter and receiver connection and start the transmission from the beginning.
The speed of a transmission is dependent upon the mode of telephone transmission. In some parts of the world, rapid information transmission is possible through telephone lines which operate in a digital mode. However, in most parts of the world, telephone lines operate in an analog mode, and therefore, their data transfer rate (bit rate) is typically limited to 9600 bits per second (bsp). The speed of a facsimile communication system is thus limited by the information capacity of the telephone lines which interfaces the facsimile machines. By utilizing high speed signal processing and efficient digital modulation techniques, the digital data transmission over analog phone lines is reaching its throughput limits.
One method commonly used which has the appearance of speeding up a facsimile transmission is the compression of the pixel data at the transmitter and the subsequent expansion of that data at the receiving end. The compression/expansion unit (CEU) of a facsimile machine operates to reduce the amount of information to be transmitted and received, however, it does not transmit information faster.